Effective models for TADF: the role of the medium polarizability

Huu, D. K. Andrea Phan; Saseendran, Sangeeth; Painelli, Anna

doi:10.1039/d1tc05296a

Cited by 17 publications

(50 citation statements)

References 55 publications

(100 reference statements)

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“…Solvatochromism, that is, the dependence of the spectral properties of dyes on the solvent, is the most obvious manifestation of the phenomenon . Models accounting for normal and inverse solvatochromism in polar dyes have been known for decades, , and more detailed treatments also accounting for the evolution of spectral band shapes have been proposed. ,, In TADF dyes, the phenomena are more complex because not just the spectra depend on the dielectric properties of the medium, , but the ST gap and the SOC are also affected with important and highly nontrivial consequences on the TADF photophysics. ,, To make the issue more complex, delayed fluorescence occurs on very long time scales that in solid matrices are possibly comparable to the matrix relaxation times, resulting in a highly nontrivial interplay of interactions.…”

Section: Methodsmentioning

confidence: 99%

“…Here we build on previous work , on a prototypical DA dye for TADF application, 9,9-dimethyl-9,10-dihydroacridin-4,6-triphenyl-1,3,5-triazine (DMAC-TRZ, Figure ), to discuss environmental effects. Specifically, we adopt the essential state model proposed and parametrized ab initio for DMAC-TRZ .…”

Section: Introductionmentioning

confidence: 99%

“…Specifically, we adopt the essential state model proposed and parametrized ab initio for DMAC-TRZ . The model is exploited to calculate RISC and ISC rates following an original strategy that fully accounts for the anharmonic and nonadiabatic vibrational and conformational motion . This sets a sound basis to address environmental effects on TADF, as needed to directly compare with experimental data.…”

Section: Introductionmentioning

confidence: 99%

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Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases

et al. 2022

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We present a detailed and comprehensive picture of the photophysics of thermally activated delayed fluorescence (TADF). The approach relies on a few-state model, parametrized ab initio on a prototypical TADF dye, that explicitly accounts for the nonadiabatic coupling between electrons and vibrational and conformational motion, crucial to properly address (reverse) intersystem crossing rates. The Onsager model is exploited to account for the medium polarity and polarizability, with careful consideration of the different time scales of relevant degrees of freedom. TADF photophysics is then quantitatively addressed in a coherent and exhaustive approach that accurately reproduces the complex temporal evolution of emission spectra in liquid solvents as well as in solid organic matrices. The different rigidity of the two environments is responsible for the appearance in matrices of important inhomogeneous broadening phenomena that are ascribed to the intertwined contribution from (quasi)static conformational and dielectric disorder.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases

et al. 2022

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“…Their methodology for the evaluation of rISC rates is also based on the definition of electronic diabats, and accounts for explicit vibrational modes, structural conformations and environmental effects. A fundamental difference with respect to our scheme is the inclusion of electronic couplings to the (diabatic) ground state accounting for nonradiative decay pathways [58,59] …”

Section: Le‐mediated Riscmentioning

confidence: 99%

“…A fundamental difference with respect to our scheme is the inclusion of electronic couplings to the (diabatic) ground state accounting for nonradiative decay pathways. [58,59] Time evolution of the three state system from 3 CT (Figure 2) shows how 3 LE catalyzes the triplet state decay, resulting in an effective rISC rate more than one order of magnitude larger than in the 2-state model (Table 1). Such an increase is recovered by the QME simulations and by inserting Marcus and BJ reaction rates in equations 5-8.…”

Section: Le-mediated Riscmentioning

confidence: 99%

Theory of Exciton Dynamics in Thermally Activated Delayed Fluorescence

Carreras

Casanova

2022

ChemPhotoChem

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Thermally activated delayed fluorescence (TADF) is an upconversion photophysical process based on the population of a bright excited singlet state from an excited triplet via reverse intersystem crossing (rISC), which might be employed to overcome the statistical limitation of electron-hole recombination in organic light-emitting diodes. In this work, we describe the intricacies of TADF dynamics by means of a quantum master equation and through perturbative approaches to rate constants of internal conversion and ISC. Simulation of the time evolution from the lowest excited triplet in systems with small energy gaps allows to disentangle the role of different electronic states mediating the population of the singlet manifold and the importance of various rISC mechanisms. Energy gaps between charge transfer (CT) and local excitons (LE), and interstate (hyperfine, spin-orbit and vibronic) couplings are key factors tuning the feasibility of rISC. Since in molecules LE/CT spin-orbit coupling is, in general, larger than hyperfine interactions, the rISC rate is largely increased in those situations where either the direct or mediated triplet-singlet interconversion between states of different character is energetically available. Interestingly, temperature dependence of rISC rate is stronger for the spin-vibronic coupling mechanism than via hyperfine interaction.

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Efficient Reverse Intersystem Crossing in Carbene‐Copper‐Amide TADF Emitters via an Intermediate Triplet State

2023

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The mechanism behind reverse intersystem crossing (rISC) in metal‐based TADF emitters is still under debate. Thermal rISC necessitates small singlet/triplet energy gaps as realized in donor‐acceptor systems with charge‐transfer excited states. However, their associated spin‐orbit couplings are too small to account for effective rISC. Here, we report the first nonadiabatic dynamics simulation of the rISC process in a carbene‐copper(I)‐carbazolyl TADF emitter. Efficient rISC on a picosecond time scale is demonstrated for an initial triplet minimum geometry that exhibits a perpendicular orientation of the ligands. The dynamics involves an intermediate higher‐lying triplet state of metal‐to‐ligand charge transfer character (3MLCT), which enables large spin‐orbit couplings with the lowest singlet charge transfer state. The mechanism is completed in the S1 state, where the complex can return to a co‐planar coordination geometry that presents high fluorescence efficiency.

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Effective models for TADF: the role of the medium polarizability

Abstract: A novel approch to estimate intersystem and reverse intersystem crossing rates (ISC and RISC rates, respectively) is proposed. We build on an essential state model recently parametrized {\it ab initio}...

Cited by 17 publications

References 55 publications

Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases

Thermally Activated Delayed Fluorescence: Polarity, Rigidity, and Disorder in Condensed Phases

Theory of Exciton Dynamics in Thermally Activated Delayed Fluorescence

Efficient Reverse Intersystem Crossing in Carbene‐Copper‐Amide TADF Emitters via an Intermediate Triplet State

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